This invention relates to an ultrasonic diagnosing apparatus of a sector scan type.
An ultrasonic probe for the sector scanning used in an ultrasonic diagnosing apparatus has a plurality of transducer elements or phased-array transducer elements 2 arranged on a damper member 1, as shown in FIG. 1. Generally, the transducer element 2 is a piezoelectric element which converts an electric signal into a mechanical vibration and vice versa. Each transducer element 2 is connected to an individual electrode 3. In practical use, the probe is placed on a body surface of a patient and is supplied with electric signals for electronically scanning a target plane in the body.
There will now be described the principle of the electronic scanning. As shown in FIG. 2, an electric signal is applied to each group of five transducer elements generally designated by 2 from left to right. Specifically, the signal is successively applied to each group or block of five elements, 2.sub.1 to 2.sub.5, 2.sub.2 to 2.sub.6, 2.sub.3 to 2.sub.7 . . . . The signals are progressively applied to the transducer elements by shifting the transducer elements 2 pitch by pitch. Therefore, the blocks each consisting of five transducer elements 2 successively shift to the right pitch by pitch as viewed in FIG. 2. Upon receipt of the signal, each element block emits an ultrasonic wave radially. The most intensive field of the ultrasonic wave is at the central part of the element block including five transducer elements. Therefore, an ultrasonic beam UB may be considered to be radiated from the transducer elements located at the central part. Each block is successively shifted to the right so that the ultrasonic beam UB also shifts to the same direction. The scanning method is called a linear scanning in which the ultrasonic beam may be considered to be radiated from the central part of the ultrasonic radiating surface of the probe which is driven sequentially in parallel. The conventional ultrasonic diagnosing apparatus is described in Uchida et al 19-33 "Electro-Scanning Ultrasonic Diagnosing Equipment", a thesis announced at the convention sponsored by Japanese Institution of Medical Ultrasonics, May, 1971. Another known scanning method is a sector scanning method in which signals with different phases are applied to corresponding blocks each consisting of, for example, five transducer elements. In this case, the most intensive field of the ultrasonic wave changes in response to pulses with the phase difference which drive the elements. Accordingly, the radiation angle of the ultrasonic beam depends on the phase difference and therefore the radiation direction of the ultrasonic beam may be changed by changing the phase difference. The sector scanning may accordingly be carried out if the phase difference is continuously changed.
The electronic scanning method at present is roughly classified into the linear scanning method in which the ultrasonic beam is shifted in parallel and a sector scanning method in which the ultrasonic beam is shifted in a sector pattern, the principle of which is disclosed in U.S. Pat. No. 3,789,833.
In the linear scanning method, the probe 4 is constructed by using a large number of transducer elements 2 horizontally arranged in parallel, as shown in FIG. 3. As described above, in this method, the scanning direction (an arrow A) of the beam UB is the same as the element arranged direction. The radiating direction of the ultrasonic beam UB is normal to the element-arranged direction.
In the sector scanning method, the probe 5 includes for example, five phased-array transducer elements 2 horizontally arranged representing each block, as shown in FIG. 4. In operation, electric signals with fixed phase differences are sequentially applied to the respective transducer elements 2 and the phase difference also is sequentially changed so that the ultrasonic beams are radially emitted with respect to the center point on the probe.
A conventional ultrasonic diagnosing apparatus for "C" mode display by the electronic scanning system, which is two-dimensional image in a plane perpendicular to the "B" mode display, generally employs the linear electronic scanning method and this is realized by a water immersing method, as shown in FIG. 5. Reference numeral 51 is a linear scanning controller for providing a control signal to control the scanning operation of the device. In response to the control signal from the controller 51, a pulse circuit produces pulse signals which are applied to a probe 54 for linear scanning in an ultrasonic wave scanner 53. Then, the probe 54 vibrates to radiate an ultrasonic wave. The probe 54 is immersed in liquid (water, liquid paraffin or the like) 56 in a water bag 55 placed on a patient 57 and the ultrasonic wave is transmitted through the liquid 56 to the patient 57 contacting the water bag 55. A part of the ultrasonic wave is reflected from a location having a different acoustic impedance in the patient body 57, and returns to the probe 54. The reflected ultrasonic wave is converted into a corresponding electrical signal. The electrical signal is supplied in accordance with a control signal from a scanning controller 51 to a receiver 58 where it is amplified and then transmitted to a gate circuit 59. The gate circuit 59 permits the passing therethrough of video signal from a depth D.sub.Z set by a depth setting circuit 60 for setting a target plane in the patient body to be displayed in "C" mode, i.e. the depth D.sub.Z from the body surface. The video signal passing through the gate circuit 59 is transferred to a monitor 61. The probe 54 is mechanically moved in a direction X of arrow within a range for a "C" mode, by means of a scanner 53. The moving position is detected by a scanning position detection circuit 62 and then is supplied to the monitor 61.
A signal which represents a position on a Y-axis in scanning is transferred from a scanning controller 51 to a monitor 61. These three signals cooperate to display a brightness-modulated image in "C" mode on a screen of the monitor 61. Specifically, assuming that the moving range of the probe 54 by the scanner 53 is represented by D.sub.X in X-axis direction, and the electronic scanning range of the probe 54 by D.sub.Y in Y-axis direction, displayed is an image on a plane S defined by D.sub.X and D.sub.Y at the depth D.sub.Z in Z-axis direction, as shown in FIG. 6.
As described above, in the conventional "C" mode display, the electronic scanning may be applicable for the Y-axis direction. For the X-axis, however, the mechanical movement by the scanner 53 must be used. It is for this reason that, by convention, the water bag 55 is used for ensuring a smooth mechanical movement of the probe and a good transmission of the ultrasonic wave. This method, however, suffers from the following disadvantages: - (1) for every observation, the water bag 55 must be replaced corresponding to the body surface configuration of the patient 57 or the target location; (2) when the body surface is uneven, the entire surface must be intimately in contact with the water bag 55. It is very difficult, however, to obtain a perfectly intimate contact therebetween. Reflection or damping of the ultrasonic wave at the poor contact location is unavoidable, resulting in deterioration of the image quality.
The contact method in which the probe is directly in contact with the body surface, has frequently been used. The linear scanning probe has a relatively large width so that it is very difficult to intimately contact the entire scanning area of the probe with the body surface. The linear scanning probe has the construction as mentioned above so that the probe width is fixed, that is to say, can not be varied. Therefore, the probe must be selected for use in accordance with the object to be observed and this is very troublesome.